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Load a single ball in the breach. Make a feed tube blocking device to prevent blowback and stick it in the feed tube far enough to use up any space but not far enough to interfere with the bolt. Fire the gun and see if the velocity is any higher without the blowback.

Except for the Automag in front, its usually the man behind the equipment that counts.

Load a single ball in the breach. Make a feed tube blocking device to prevent blowback and stick it in the feed tube far enough to use up any space but not far enough to interfere with the bolt. Fire the gun and see if the velocity is any higher without the blowback.

Now why would you go and state something obvious like that? Definitely worth a try.

But seriously, I need to step away from this for a couple days to let the fog clear.

The only question I have is I originally came up with this concept when comparing it to an Autococker. If the balls seats in the barrel (let's not talk about how to properly size it, lol), say an inch away from the ideal location, velocity can vary. Applying that to this situation, if the air blast is released too far behind the ball, would the feed tube blocking device be a conclusive test? Regardless, please try it if anyone is willing.

Also, this won't help if the air blast is not concentrated on the center of the ball, which is my hypothesis of the day, (er...evening, alright hour).

The only question I have is I originally came up with this concept when comparing it to an Autococker. If the balls seats in the barrel (let's not talk about how to properly size it, lol), say an inch away from the ideal location, velocity can vary. Applying that to this situation, if the air blast is released too far behind the ball, would the feed tube blocking device be a conclusive test? Regardless, please try it if anyone is willing.

Also, this won't help if the air blast is not concentrated on the center of the ball, which is my hypothesis of the day, (er...evening, alright hour).

There would be variances depending on the distance from the tip of the bolt. The test won't be ideal, but should help determine if that much air is actually going up the feed tube instead of pushing the ball out the barrel.

The air doesn't have to be centered behind the ball. The air will fill the void behind the ball before any real effect can be felt by the ball anyway. The air pressure behind the ball will generally be in the vicinity of 60psi before there is noticeable movement in the ball, due to the mass of the ball and the inertia the air pressure needs to overcome.

The air doesn't have to be centered behind the ball. The air will fill the void behind the ball before any real effect can be felt by the ball anyway. The air pressure behind the ball will generally be in the vicinity of 60psi before there is noticeable movement in the ball, due to the mass of the ball and the inertia the air pressure needs to overcome.

OK, I'll buy that if the feed tube is sealed off, which is what we were discussing.

What I should have said was the test won't determine if the ball, barrel, and bolt axes are aligned.

So, seal off feed tube, and measure velocities of a string of shots with the marker tipped back (ball against bolt face) and marker tipped forward (ball against detent). This should give us the data to see the effect of sealing off the feed tube and the effect of distance from power pulse (if the bolt isn't already pushing the ball before the power pulse is released).

From there, a fairly simple set of measurements will tell if the axes are aligned, which will matter if the feed tube is not sealed off, since pressure takes path of least resistance.

the feed port does not appear to be on center of the feed block in most of the pictures I am seeing. What about the possibility that the feed port is in the wrong place? That would put it in the wrong location in relation to the bolt face. I don't know the order of operations they used for making the feed block, but if they put the key and boss on the wrong ends after machining the feed port it would probably move the feed port about that much.

Its easy to check. Measure the front of the feed block to the front of the feed tube and compare between OPBN and Sniper42. A ruler would work, its more than 1/8" its out.

Either that or all of the machining on the bottom face is set .150 to far to the rear. That would also require that the sear hole was buggered too. I can't see it firing if the sear hole was in the correct position and the frame and valve were trailing by .150. I seem to remember a video of these being manufactured on a 4th axis, so I can't see this being likely. Unless its a setup part that should have been scrapped out.

Having the bore from the back be .150" deeper than others shouldn't make any more difference than a softer spring would. It should in theory allow the bolt to travel farther forward past the feed port than it needs to, not allow it to set back farther.

the feed port does not appear to be on center of the feed block in most of the pictures I am seeing. What about the possibility that the feed port is in the wrong place? That would put it in the wrong location in relation to the bolt face. I don't know the order of operations they used for making the feed block, but if they put the key and boss on the wrong ends after machining the feed port it would probably move the feed port about that much.

I agree, and this would lead to my aforementioned autococker-with-ball-partly-down-the-barrel-resulting-in-low-velocity analogy, correct?

Its easy to check. Measure the front of the feed block to the front of the feed tube and compare between OPBN and Sniper42. A ruler would work, its more than 1/8" its out.

I agree. We're building quite a list for these two volunteers.

Either that or all of the machining on the bottom face is set .150 to far to the rear. That would also require that the sear hole was buggered too. I can't see it firing if the sear hole was in the correct position and the frame and valve were trailing by .150. I seem to remember a video of these being manufactured on a 4th axis, so I can't see this being likely. Unless its a setup part that should have been scrapped out.

I would love to get my hands on the process sheets/drawings. It all depends what they used for datums for all the various features.

Having the bore from the back be .150" deeper than others shouldn't make any more difference than a softer spring would. It should in theory allow the bolt to travel farther forward past the feed port than it needs to, not allow it to set back farther.I agree. However, my hypothesis isn't about the distance from rear field strip screw hole to bolt spring seat. It is about the distance from rear field strip screw hole to breech and other features all from the same datum - the rear field strip screw. See my list of dimensions I would like to gather from various bodies in this thread: http://www.automags.org/forums/showt...-2k9-mag/page2 We have not yet verified these are the same between functioning and non-functioning bodies. If the bolt releases the power pulse too soon relative to the breech/barrel geometry, it could lose much of the pressure up the feed tube.

The field strip hole should probably be the datum, but you are looking at it backwards. The valve will always release at a given point of travel of the bolt. It you let it go further, it does not release any earlier. It releases exactly where it is supposed to. If the bore is deeper it only results in less spring pressure and possible over travel. Over travel should only result in the bolt face stopping further into the breech. You *might* get some blowback from over travel of the bolt if the pressure worked its way around the rear flange of the bolt..... but that's not any different than a normal situation. Under travel would be an entirely different story. Worst case the bolt does not travel far enough to break the seal and you have bolt stick until it bleeds off, or it does break the seal and you have massive blowback from an open breech.

From what I remember reading, the bolt face is sitting .150 back from the rear edge of the feed port. It should be sitting nearly flush. Since the travel of the bolt is what seals the breech and releases the pressure, the pressure is released .150 before the breech is sealed ( its probably some amount smaller than that). Its releasing the pressure when its supposed to. it just doesn't have a closed breech. Having a deeper hole for the spring to sit in won't cause that. Having the feed port out of position to the field strip hole definitely will.

Its got be either the feed port location or the field strip hole location. I would suspect that all of the holes on the bottom were machined in one operation ( that's what I would have done). If the field strip hole is out, all of the holes should be out and the barrel block should not be able to be installed ( the holes in the body would not match up to the holes in the block when placed on the body). If the feed port is out, its would only affect the feed port and everything would still go together properly. But it won't work right.

IF the depth of that hole were overly critical they would not have been able to send out washers to put in there after the fact.

Larger feedport? that should put your bolt face1/8" into your breech. other than possible feed problems due to a lack of space for the ball to feed, a shorter spacing should work. a longer spacing is where you will start to find blowback problems.

And i may have missed it, but is your micro having problems too? i thougt you two were comparing because yours worked and his didnt. comparing two that don't would be somewhat futile lol.

The field strip hole should probably be the datum, but you are looking at it backwards. The valve will always release at a given point of travel of the bolt. It you let it go further, it does not release any earlier. It releases exactly where it is supposed to. If the bore is deeper it only results in less spring pressure and possible over travel. Over travel should only result in the bolt face stopping further into the breech. You *might* get some blowback from over travel of the bolt if the pressure worked its way around the rear flange of the bolt..... but that's not any different than a normal situation. Under travel would be an entirely different story. Worst case the bolt does not travel far enough to break the seal and you have bolt stick until it bleeds off, or it does break the seal and you have massive blowback from an open breech.

From what I remember reading, the bolt face is sitting .150 back from the rear edge of the feed port. It should be sitting nearly flush. Since the travel of the bolt is what seals the breech and releases the pressure, the pressure is released .150 before the breech is sealed ( its probably some amount smaller than that). Its releasing the pressure when its supposed to. it just doesn't have a closed breech. Having a deeper hole for the spring to sit in won't cause that. Having the feed port out of position to the field strip hole definitely will.

Its got be either the feed port location or the field strip hole location. I would suspect that all of the holes on the bottom were machined in one operation ( that's what I would have done). If the field strip hole is out, all of the holes should be out and the barrel block should not be able to be installed ( the holes in the body would not match up to the holes in the block when placed on the body). If the feed port is out, its would only affect the feed port and everything would still go together properly. But it won't work right.

IF the depth of that hole were overly critical they would not have been able to send out washers to put in there after the fact.

I agree with this in its entirety. I misread your earlier post that I originally disagreed with. I have corrected that post. If you could requote me, so as not to confuse others that read this thread, I would greatly appreciate it. You will see from the date and times of my posts in the other linked thread that we have been on the same page all along.

Sorry for the confusion; I need to quit the 3:30am-11pm days I've been pulling thanks to my teething 15 month old.

Larger feedport? that should put your bolt face1/8" into your breech. other than possible feed problems due to a lack of space for the ball to feed, a shorter spacing should work. a longer spacing is where you will start to find blowback problems.

And i may have missed it, but is your micro having problems too? i thougt you two were comparing because yours worked and his didnt. comparing two that don't would be somewhat futile lol.

OPBN's works, but his shoots a ball out of the feed tube as well, when a single ball is set on top of a chambered ball, and the chambered ball fired without a hopper on.

I'm trying to put a quick sketch together using AGD CAD dimensions, OPBN's dimensions, and sniper42's dimensions. I think there's enough here to show different degrees of feed tube blow out. If you recall from one of my previous posts, I can stack two balls on top of a chambered ball, and the top ball barely jostles in both my ULE body and X-Mag.

Larger feedport? that should put your bolt face1/8" into your breech. other than possible feed problems due to a lack of space for the ball to feed, a shorter spacing should work. a longer spacing is where you will start to find blowback problems.

And i may have missed it, but is your micro having problems too? i thougt you two were comparing because yours worked and his didnt. comparing two that don't would be somewhat futile lol.

No mine works fine. Sniper needs to provide this measurement. The ULE, TAC, & MM2K9 all have Angel threaded feednecks, so the holes should be the same size.

So it seems my feed hole is indeed too far forward. It is about 3.65" from the back of the feedhole to the field strip screw. That most likely is what is causing the blowback up the feedstack and the low velocity.

I'm trying to put a quick sketch together using AGD CAD dimensions, OPBN's dimensions, and sniper42's dimensions. I think there's enough here to show different degrees of feed tube blow out. If you recall from one of my previous posts, I can stack two balls on top of a chambered ball, and the top ball barely jostles in both my ULE body and X-Mag.

So we need to:
1. Confirm Henchman's measurements. The ones he posted in the other thread were to the bolt spring seat, not the feed tube edge.
2. Confirm OPBN's measurements. The AGD body is different from all the other AGD bodies. The MM2K9 appears the same as most stock AGD bodies, but if there is some other design difference, it could accout for the blowout...or the measurement needs to be verified...lol
3. Confirm sniper42 friend's body has the same ball blowout issue from the feed tube.
4. Confirm Dukie's bodies have no ball blowout from feed tube.
5. See if increasing deviations from AGD stock bodies cause increasing amounts of feed tube blowout. Does the ball fly up further as the 3.5" dimension increases?

Last edited by nak81783; 08-05-2013 at 01:22 PM.
Reason: Updated with info from subsequent posts

So it seems my feed hole is indeed too far forward. It is about 3.65" from the back of the feedhole to the field strip screw. That most likely is what is causing the blowback up the feedstack and the low velocity.

How can this be though? With a ball in the breach and pushing on the détents we have the same amount of space between the ball and bolt face.

And my measurements were from the back of the feed hole( I used a straight edge to line up with the back side of the feednecks) and the center of the FS hole. I will have some time tomorrow to do some masking off so show my measurements are "on".

I have no blowback issues on any of mine. i can fire 2 balls in the feed port without launching #2 out the top. mind toy the classic is a pf, and the minimag is a vert conversion.

It might be a good idea to also get a measurement of center of field strip to rear of feed block. that should confirm weather the feedblock is the issue or the bottom drilling / milling.

I am betting on the feedblock being machined backwards. that at least should be a relatively easy fix. just get a good one.

However..... the bottom frame screw and sear milling beeing out of position would also explain the extra .150 od depth in the bore. that would suck. i still dont buy it though. why do two complete setups for holes on the same face? thats silly. if it is that it could be fixed with a custom breech.

How can this be though? With a ball in the breach and pushing on the détents we have the same amount of space between the ball and bolt face.

And my measurements were from the back of the feed hole( I used a straight edge to line up with the back side of the feednecks) and the center of the FS hole. I will have some time tomorrow to do some masking off so show my measurements are "on".

The scenario i can see- material roughed and feed port machined. part loaded backwards and the front-or- rear features were milled. opposite end milled. the part is now correct except for the feedport being on the wrong side of center. part loaded correctly since it is now obvious, (and the keying feature on the front was probably used,) detent holes machined. that would put the detent holes in the correct location in regards to bolt face, leaving the feedport incorrect.

All of that is provided they didnt use a fourth or fifth axis. i remember the delays due to some big orders that came in. these may have been pushed on to a 3 axis machine which would mean many more operations and chances for mistakes.

Alright, I pulled my feedneck off and did some further gleening. On my MM2K9, the feed neck hole/port is not centered from front to back. It sits farther to the back of the breach than the front. Sniper or whomever else, where does yours sit? I am trying to measure it, but its a bit difficult because the edge of the hole is beveled inward.